Parageneses of Ordovician sub-greenschist to greenschist facies metabasites from Wales, U.K.

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doi: 10.1127/ejm/5/5/0925
Authors:Bevins, Richard E.; Robinson, Douglas
Author Affiliations:Primary:
National Museum of Wales, Department of Geology, Cardiff, United Kingdom
Other:
University of Bristol, United Kingdom
Volume Title:European Journal of Mineralogy
Source:European Journal of Mineralogy, 5(5), p.925-935. Publisher: Schweizerbart'sche Verlagsbuchhandlung (Nägele u. Obermiller), Stuttgart, Federal Republic of Germany. ISSN: 0935-1221
Publication Date:1993
Note:In English. 29 refs.; illus. incl. 1 table, geol. sketch maps
Summary:The pattern of mineral parageneses developed in Wales indicates that there is a lower-grade assemblage with abundant prehnite and pumpellyite, associated with pelites showing diagenetic to anchizone illite crystallinity values, whereas higher-grade assemblages contain actinolite in the absence of both prehnite and pumpellyite, i.e. classic greenschist facies. In the transition zone there is a strong whole-rock compositional control, in particular MgO/(MgO+FeO) ratios, on mineral parageneses. The occurrence of prehnite-pumpellyite facies assemblages in areas of diagenetic illite crystallinities and regular mixed-layer phyllosilicates suggests that the onset of the anchizone and the prehnite-pumpellyite facies are not directly linked in Wales. The appearance of stilpnomelane in both anchizone and epizone conditions in metabasites in which MgO/(MgO+FeO)Chl ratios are < 0.32 is noted. [R.A.H.]
Subjects:Chain silicates; Facies; Greenschist facies; Metabasite; Metaigneous rocks; Metamorphic rocks; Mineral assemblages; Ordovician; Orthosilicates; P-T conditions; Paleozoic; Paragenesis; Phase equilibria; Prehnite; Pumpellyite; Pumpellyite group; Silicates; Sorosilicates; Europe; Great Britain; United Kingdom; Wales; Western Europe
Abstract Numbers:94M/2535
Record ID:1993041702
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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